Not sure what you mean witth 'load test'... if you need to perform stress tests on your server, you'll probably find several (non-OutSystems) tools for doing that.

However, if you just need to get some useful performance indicators, then go to Service Center > Analytics tab. You can generate reports for slow queries, slow screens, slow web services, etc... This data is present in the platform's datamodel, so you can also access it by referencing the '(System)' eSpace and consuming the Report* entities (may be useful if you want to build your own tool for analyzing performance).

You can also get some useful info from performance counters, such as:
- \Processor(_Total)\% Processor Time
- \Memory\Pages/sec
- \PhysicalDisk\Avg. Disk Queue Length
- \TCPv4\Connections Established